Processing units (PUs) execute instructions to read, manipulate, and write data. Both the instructions and data are commonly stored in a separate memory, which is coupled to the PU via a communication channel. In a common example, a personal computer (PC) normally includes a central processing unit (CPU) coupled to a quantity of dynamic, random-access memory (DRAM) via a channel called a “memory bus.”
The speed at which a PU can process instructions depends in part on how fast the memory is able to read and write instructions and data, which in turn depends in part on the speed with which signals can be communicated over the memory bus. Faster computers require faster memory buses, so a considerable amount of resources have been expended improving the speed performance of memory buses.
Memory buses are commonly “multi-drop,” which means that a number of memory devices can share the same channel. Multi-drop buses are desirable because they allow manufactures and users the flexibility to provide different types and amounts of memory. However, multi-drop buses tend to degrade memory signals, and thus reduce speed performance. An alternative to multi-drop buses, so-called “point-to-point” connections, directly connect the PU to the one or more memories, and thus avoid signal degradation that result from bus sharing. The problem with these systems is that point-to-point connection resources are wasted unless the memory system has the maximum number of memories. In a topology that supports two memory modules, for example, half the point-to-point interconnects would be wasted in a one-module configuration.
The assignee of the instant application developed “Dynamic Point-to-Point (DPP)” memory-bus technologies that allow manufacturers and users of computer systems the flexibility to provide different numbers of memory modules in a manner similar to multi-drop buses but without the wasted connection resources that can result in conventional point-to-point. In DPP memory topologies, the same number of point-to-point connections is used for different numbers of memories. Most memories and memory systems do not support DPP connectivity, and thus lack the benefits of these systems. There is therefore a need for methods and circuits for extending the advantages of DPP to additional types of memory resources.
The figures are illustrations by way of example, and not by way of limitation. Like reference numerals in the figures refer to similar elements.